Click Steam in the top-left corner and select Exit . Do not just click the "X" button.
: Ensure both "Steam" and "Steam web helper" are allowed through the Windows Firewall Advanced Solutions Opt-in/Out of Steam Beta : Some users resolved the issue by going to Beta participation just cause 4 unable to initialize steam api
If these fail, collect the game's log files (install folder and %LOCALAPPDATA%\JustCause4) and post the exact error text and your OS, Steam client version, and whether you use any mods—I'll suggest next steps. Click Steam in the top-left corner and select Exit